Investigations of Hyporheic Temperature Regimes in Arctic Alaska Streams Using Time Series Analysis Techniques

1 Univeristy of Colorado-Boulder2 Colorado School of Mines3 Univeristy of Colorado-Boulder4 Boise State University5 Boise State University6 Boise State University7 University of Vermont

Stream and hyporheic temperatures are important characteristics of stream ecosystems, influencing the distribution and survival of aquatic organisms as well as the rates of biogeochemical reactions. In this study we use time series analysis techniques, such as Fourier analysis, to examine the hyporheic thermal regimes of streams in Arctic Alaska to detect frequencies of recurrence and factors that may be controlling those frequencies. We propose that
temporally offset, but detectable frequencies between depths will be indicative of exchange of water between the stream and the streambed. Preliminary work has identified cycles occurring at
subdaily, daily, and longer timescales that could be linked to hyporheic exchange, air temperature, radiation, stream discharge, and rainfall events. Initial results indicate that the daily
temperature signal is significantly dampened with depth while signals at longer timescales are not dampened as severely and may, in some cases, increase. Because the temperature signals are not perfect sine waves, some of the frequencies emerging from the Fourier analyses may not be indicative of separate cycles in and of themselves but rather may help characterize the asymmetrical shape of the dominant frequencies. Time series records that we have/will analyze include those for thermocouple strings measuring temperatures at five different depths below the streambed surface as well as records from a nearby meteorological station.